The goals of this research are to study the responses of infant Indian langur monkeys (Presbytis entellus) to the loss of major caretakers--first the mother and then an adopted caretaker--and to search for those factors which influence the infant's reactions to loss. Langurs offer a unique opportunity for the investigation of separation anxiety and depression or distress following loss because the infant langur has multiple important caretakers from the day of birth. The langur provides a very different model for the investigation of reaction to loss than that of the well-studied macaques. The proposed research will seek to determine the strength and nature of the attachment a langur infant has to its mother and subsequently to the adult the infant adopts during its mother's absence. Preliminary investigation reveals a high proportion of permanent infant initiated adoptions following mother-loss. The reaction of infant langurs to separation varies from slight to significant distress. Factors such as early maternal restrictiveness, availability of receptive substitute caretakers, sex differences, and early experiences with siblings, caretakers, and peers will be studied to understand the infant's coping reactions during loss. Data are gathered by use of a focal animal sampling technique, and each animal in the colony is sampled regularly to maintain a continuous, baseline data record. All animals born into the colony groups have been sampled from the day of birth.